It is an ongoing trend that mobile electronic devices offer image capture capability. Some mobile electronic devices, such as a cellular phone, can capture images from both a front and a back side of the device. Many solutions exist for such dual facing camera capability. Solutions typically use two image sensors on opposing sides of the device.
Image sensors are integrated circuits (ICs) used to detect and measure radiation, such as light, received by the sensor device. A front-side illuminated (FSI) image sensor typically has pixel circuitry and metal stacks disposed on a front side of a substrate where a photosensitive or photodiode (“PD”) region resides. To form an image in the PD region, the radiation passes the metal stacks. A backside-illuminated (BSI) image sensor, on the other hand, is typically formed on a thin substrate that allows the radiation to reach the PD region by passing through the substrate. A BSI image sensor offers many advantages over an FSI image sensor, such as shorter optical paths, higher quantum efficiency (QE), higher image resolution, smaller die sizes, etc.